Today I rode past a billboard advertising a Jeep SUV of some sort, proclaiming the beast gets 39 miles per gallon. That’s not too shabby — build a carpool around that vehicle and you have decent efficiency. It made me wonder, as I pedaled along: what sort of mileage am I getting?

Strava estimates that at my rather-slow cruising speed along a straight, flat road (fair for comparing “highway mileage”) I’m putting out about 150 watts of effort (or less, but I’m rounding in favor of cars). Pessimistically I’m burning about five times that in stored food energy (my gasoline equivalent); the rest of the energy winds up as heat in my muscles. So I’m consuming about 750 watts to roll along at 15 miles per hour. That’s fifteen miles for 750 watt-hours, or 20 miles for one kilowatt-hour.

A gallon of gas has the energy equivalent of about 37 kWh, so were I running on gasoline, I’d get about 20 x 37 miles, or roughly 740 miles per gallon — let’s call it 700 to avoid any pretense of precision.

700 mpg! Not bad! If I lost a little more weight my mileage would get even better (or more likely I’d just ride faster).